The present invention relates to compositions and a method for the hydraulic fracturing of subterranean formations penetrated by a well. Particularly, the present invention relates to the use of alcohols, especially anhydrous alcohols, thickened with aminomethylated polyacrylamide as hydraulic fracturing fluids.
Hydraulic fracturing is an extensively employed method for stimulating the production of petroleum and natural gas from subterranean formations. The method generally involves contacting the subterranean well formation with the fracturing fluid, applying sufficient pressure to the fracturing fluid to open a fracture in the subterranean formation, and maintaining this pressure while injecting the fracturing fluid into the fracture at a sufficient rate to extend the fracture into the subterranean form.
It is desired that the fracturing fluid be viscous in nature since this will permit the fracturing fluid to remain in the fracture long enough to permit buildup and maintenance of sufficient pressure to open a fracture. Moreover, a viscous fracturing fluid is capable of supporting propping agents, which are particulated solids suspended in the fracturing fluid for the purpose of maintaining the fracture in an open condition, by being deposited in the fracture once created. Generally, it is desired that the fracturing fluid have a viscosity of at least about 25 centipoises, as measured by Fann Model 35 Viscometer at 26.degree. C. and at 100 r.p.m., for a 1.0% by weight concentration of thickening agent.
While a variety of base liquids have been employed in fracturing fluids, including water, crude oil and kerosene, alcohols have recently been employed as such base liquids, particularly in the fracturing of formations producing natural gas. Since it has been recognized that water often reduces the permeability of the particular subterranean formations involved, and can itself block access of the gas to the well bore, it has become desirable to employ anhydrous alcohols; that is, alcohols which are substantially devoid of water, as fracturing fluid base liquids.
Many materials currently available for gelling alcohols require that a significant amount of water be present in the alcohol in order for thickening to occur. Thus, the use of alcohol-water gels as fracturing fluids is often encountered. However, in view of the undesirable aspects of using water discussed above, a definite need exists in the art for materials that will thicken or gel anhydrous alcohols.
However, notwithstanding the preferred use of the thickening agents of the present invention to thicken anhydrous alcohols, they may also be successfully employed to thicken or gel mixtures of alcohols and water, in virtually all proportions of the components, where use of alcohol and water fracturing fluids is not subject to some of the disadvantages discussed above.
Polyacrylamide has been suggested as a composition suitable for gelling a number of different fracturing fluids, including alcohols. See U.S. Pat. No. 3,310,112.